We plan to complete our work on the biochemical effects of human alpha-lymphotoxin (LT) on target-cell plasma membranes. This lymphokine is a putative mediator of cell-mediated cytotoxicity, an essential component of tumor immunity. Since we have already demonstrated (by metabolic prelabeling) marked reductions in plasma-membrane protein during extensive target-cell lysis, we now intend (via surface-labeling techniques) to examine sequential membrane changes, commencing from the moment of adding LT to the time of target lysis, analyzing plasma-membrane protein, glycoprotein, and glycolipid. Using surface labeling, we will subsequently study possible consecutive plasma-membrane alterations induced in chemically altered autologous targets by sensitized human T lymphocytes. In the human T-cell experiments, we will first use trinitrophenol-modified autologous human targets, which appear to be handled by the same cellular immune response as are autologous neoplasms. These human target cells are readily available, and in this system, better controls can be attained than with human tumors. Also, the experimental conditions are more reproducible than those using freshly isolated neoplastic cells. However, subsequently we will attempt to verify the salient points thus gathered in a model utilizing freshly isolated human cancer cells. In this respect, we have recently developed a culture procedure with freshly isolated primary human breast carcinomas. Because many biol gically active substances also regulate their synthesis, we wish to determine whether the production of lymphotoxin is regulated by a feedback mechanism or modulates the generation of cytotoxic T cells. Since we have shown that human alpha-LT is a product of T lymphocytes, we hope to identify the subpopulations of T cells from which the lymphokine is derived. We are therefore fractionating human T cells into subpopulations according to their Fc receptors. Moreover, we will determine whether the subpopulation(s) of human T cells producing lymphotoxin is the same as that which constitutes the killer population in cell-mediated cytotoxicity.